I will tell you what I tried when I was 22, and what I wish I had been told instead.
I was doing weight lifting and ended up developing really bad RSI. Most likely from a combination of a few things including excessive computer use. I stopped, and after that started running, not particularly successfully. That was on and off but not very successful.
Some things I did were good, others weren't. My hips started tightening up and I had joint issues. Lots of testing and alternations later:
#1 Don't eat processed foods or things that will cause a blood sugar crash. This messes up your energy levels and makes consistent exercise much harder. Bulking up, I don't have a good answer for, other than most Westerners are far, far larger than a human would be on a normal diet. Whether or not 61kg is too skinny depends in part on your height.
#2 Get a standing desk, and use it at least part of the day.
#3 Walk every day for at least an hour (much easier if you are in a walkable city; if I wasn't, I might consider a treadmill desk)
#4 Start doing body weight exercise - I recommend "You Are Your Own Gym" for an easy start. This means you can't make up an excuse to not go to the gym because you can do it right by your desk. In this case, it cured my RSI within weeks. Definitely one of the most incredible things that has happened in my life and completely unexpected.
#5 Use an elliptical for endurance or run occasionally.
The important thing is to build up your strength and flexibility without injuring yourself. You are 22 now, but consider if you will be able to do this stuff for the next 50 years.
This baseline fitness will also make it easier to do more active things without getting tired, whether it is mountain biking, running, kayaking, skating, tennis etc.